1. Field of the Invention
This invention relates to a hydroformylation process and, more particularly, to a hydroformylation process which comprises reacting a compound of the general formula EQU CH.sub.2 .dbd.CH--CH.sub.2 --A--CH.sub.2 --X (I)
wherein X is a hydroxyl or formyl group and A is a group of the formula EQU --(CH.sub.2).sub.n -- or --(CH.sub.2).sub.m --CH.dbd.CH--
in which n is an integer of 3-8 and m is an integer of 0-5, with a mixture of hydrogen and carbon monoxide in the presence of a rhodium compound and a specific tris(substituted phenyl) phosphite.
2. Description of the Related Art
It is known that reaction of octa-2,7-dien-1-ol with a mixture of hydrogen and carbon monoxide in an organic solvent in the presence of a rhodium catalyst and a monodentate tertiary organic phosphorus compound such as triphenylphosphine or triphenyl phosphite gives 9-hydroxy-7-nonen-1-al (cf. U.S. Pat. No. 4,420,640). It is also known that hydroformylation of 7-octen-1-al in the presence of a rhodium complex and the sodium, potassium or lithium salt of m-(diphenylphosphino)benzenesulfonic acid gives 1,9-nonanedial (cf. U.S. Pat. No. 4,510,332).
Since rhodium catalysts are very expensive, it is strongly desired from the industrial standpoint that they should be used in quantities as small as possible. However, when the productivity per gram atom of rhodium is low, rhodium catalysts must necessarily be used in increased amounts. From the economical viewpoint, it is therefore required that rhodium catalysts should be recycled repeatedly for a prolonged period of time. The hydroformylation products from the compounds of the above general formula (I) are compounds each having a high boiling point. Thus, for instance, hydroformylation of octa-2,7-dien-1-ol gives 9-hydroxy-7-nonen-1-al and so on as hydroformylation products and hydroformylation of 7-octen-1-al gives 1,9-nonanedial and so on as hydroformylation products. In the process for the production of 9-hydroxy-7-nonen-1-al as desclosed in U.S. Pat. No. 4,420,640, the catalyst activity is not very high and, therefore, use of the rhodium catalyst in relatively high concentrations and recycling and reusing of said catalyst over a long period are desired for carrying out the hydroformylation reaction commercially while maintaining the rate of reaction at sufficiently high levels. However, when the hydroformylation reaction mixture is subjected to distillation for the separation of the high-boiling hydroformylation products, the catalyst in the reaction mixture undergoes thermal degradation and, further, the catalytic activity of the catalyst lowers due to accumulation of high-boiling byproducts. As a result, the cost of catalysts inevitably constitutes a high percentage of the production cost. For avoiding the above problems, U.S. Pat. No. 4,510,332 proposes a method which comprises subjecting the hydroformylation reaction mixture to extraction to thereby separate the catalyst from the reaction product. However, even when this method is emplyed, the rhodium catalyst is required to be present in relatively high concentrations in the reaction system to be carried out at a rate of reaction which is satisfactory from the industrial viewpoint.
On the other hand, U.S. Pat. No. 4,467,116 describes a hydroformylation process which comprises reacting an olefin having a group of the formula ##STR1## wherein R' is a hydrocarbyl group and the valence bond shown forms part of a hydrocarbyl group or R' together with the valence bond shown represents a ring structure having at least 5 carbon atoms in the ring, for example 2-methyl-1-hexene, limonene or methylenecyclohexane, or an olefin having a group of the formula EQU R'--CH.dbd.CH--
wherein R' is as defined above, for example cyclohexene, with carbon monoxide and hydrogen at a temperature within the range of about 50.degree.-200.degree. C. and a pressure within the range of 2-50 bars in the presence of a hydroformylation catalyst modified with an aromatic phosphite having a specific structure, such as tris(2-t-butylphenyl) phosphite or tris(2-t-butyl-4-methylphenyl) phosphite. However, the above-cited patent specification makes no mention of the applicability of the above hydroformylation process to compounds having an unsubstituted vinyl group and a functional group such as a hydroxyl or formyl group which are other than the olefins having the specific structure mentioned above. Although said specification mentions that there is a vast difference in reactivity between various olefins under similar reaction conditions using an identical catalyst system, this is a well-known fact in the art.